1. Field of the Invention
This invention relates to a low temperature process for separation of a gaseous mixture into fractions. A gaseous mixture containing components of different boiling points, all of which are below 32.degree. F at atmospheric pressure, is passed through a sequence of partial liquefaction, rectification, and separation steps, characterized by high thermal efficiency and low power requirements, to effect separation of the mixture into streams enriched with their respective components.
2. Description of the Prior Art
Numerous methods are known in the prior art involving the separation of gases. A particular method for the separation of ethylene from a gaseous stream comprising carbon dioxide, hydrogen, and low-boiling hydrocarbons is given in U.S. Pat. No. 3,729,944. The method utilizes an expanded tail gas and its equilibrium liquid as refrigerants.
Dephlegmators themselves are not new to the art. U.S. Pat. No. 2,582,068 describes an arrangement applicable to the separation of binary mixtures, whereby three dephlegmators are charged with a feed gas in parallel and the vapors discharged from their overhead are combined and sent to one or more additional dephlegmators in series.
The prior art process is particularly directed to separating a binary mixture that is available at a high initial pressure when it is desired to recover the more volatile component at substantially that initial pressure. The less volatile component is expanded to about atmospheric pressure to supply refrigeration to make up for heat leakage and other thermodynamic losses. This method is said to be especially useful for separating hydrogen and methane, since these two components have widely separated boiling points.